Steel strip tempering



Patented July 6, 1948 Isi' iiiitjsr'rR TEMPERINQ ration of New Jersey at Drawing. Application February 21,1945,

U Serial No. 579,153

1 Claim. (Cl.-148-''12) ini/ention is concerned with the art of tempering annealed cold reduced wide steel. stripiin tin..pl ate gages and made of basic open-hearth steeljfoi tin plate composition.

Tnose unfamiliar with this art'should refer to pagesi227 throughl309 of the Making, shapiiigarid Treating ofsteel'ji fifth edition, published by the CariiegieeIllinois,,Steel Corporation, this specification using the same; termsas are used-by this textf These pages giveaiwellrounded outline 'of'the art but do require amplification --to the extent of explaining that regardless of the chemical composition of the steel made into the cold reduced wide steelstrip, after it-isanhealed to a-dead soft condition andis thoroughly cleaned and ready for-tempering;-the tempering of the strip in the-cold rolling temper mill must be done with both the strip-and the temper mill rolls completelydry to avoid soiling or rusting the strip. In addition, it is better to explain that when the four-high 'rnills, which must be used-to work wide steel strip in tin plate. gages-are lubricated-by-means of liquid lubricants, the friction between the working rolls and the strip is greatly reduced so that it is not very diflicult to plastically deform the-strip, but while such lubricatiori is possible in the case: of the cold reduction mills, it cannctbe resortedto-inthe case of the temper mills because of the necessity for producingacoma pletely clean strip as previously" explained, "so in the case of temper: cold rolling thelfriction between the working rolls and thestrip is very high and it is very difiicult to eiTe-ct even the very slight amount of plastic deformation of the strip necessary to put the coldr workwstrain into it required to provide the tempers now currently demanded by the users of tin mill products in general and tin plate in particular.

New in addition to the above-thetiri can manuiacurers, who use most of the coldQrediiced tin plate produced, in some instances have come to the opinion that the steel from which tin plate is made should have a chemical composition that is very low in all the metalloids commonly specified and considered in the case of basic openhearth plain carbon steel from which cold reduced tin plate is made, so it is not possible to run the hardening alloys up a little above what is common in basic open-hearth steel, such as by resorting to high phosphorus for example, even though this would aid in procuring the higher tin plate tempers now also being demanded simultaneously with the requirement for low metalloids again by some of the can manufacturers. That is to say, basic open-hearth steel rephosphorized to give it 'wphosphorus content in the neighborhood'of that common to Bessemer steel, greatlyiacilitates temper rolling of the steel to high tin plate tempers andwhilethis-practice was resorted to in thepast-it is no longer'possible because of the requirement'for very low phosphorus in tin plate te l i1. J

The-presentinvention was-especially developed tomeet the requirements i or a 'mii'iimunrl temper representedby-a surface hardnes's' of atleast about--61Rockwell T BO, 'in-the" case of cold reduced tin plate made from steel containing from .05 to-.12% carbon;:' from- .25- to -.60'% manganese, notmore than .015% ph'osphorusy-not more than -.050%sulphur;not more-than .0l0% silicon, not more=tharr-;060'%" c0pper; not more than 114% nickel, n'ot moreithari .06% chromium; not more than .0-2%-- arsenic =and=not more than 115% molybdenum. It is to be observed that-this steel is not onlylow in-"phosphorus' and the other nictalloi-ds usually"considered in 'th'e case of plain carbon' steel; but also that it is very low in all of those alloys not usually specified-in the caseof plain carbon steel but whichare presentias residuals resulting from their unintentional prcsence in currently availablewsteel :makingiamaterials. With a this particular composition, the described surface-hardness can be :given :the' dead a soft anhealed coid reduced wide steel stripiiini tin plate gages from which ithewtin :plate mustbe made, by. coldirolling it inia -t'emperi milLwbutmore than one rollingipass is required and sometimes" other expe'dients :must'be used,=ithis increasingsthe cost of making -the" tin plate; to an. undesirable extent. Accord-ing to the present invention, duringfthe making oithetabove steel, nitrogen is:added 'to it to -provide theranneale'd cold reduced 'lwide steel strip; which must lee-tempered, withi'a minimum nitrogemcontent'oi -08 this being done-by any propersteel .-.making. practice so i as: to i give the d'efihed'chemical' composition to thefinished steel excepting that it will also contain at least the .008% nitrogen described. The steel making art is at a stage where steel makers are fully aware of how to make the steel by the basic open-hearth process so as to finish it with this nitrogen content and otherwise with the composition de scribed.

After the steel is finished it goes through th remainder of the steps described in the defined text as required to process it to completely cleaned annealed cold reduced wide steel strip in tin plate gages, when it naturally has the described chemical composition. At this time it has a surface hardness appreciably less than the to at least this defined surface hardness.

3 61 Rockwell T-30 required as the minimum temper, so it is then, as the next step in its tempering, dry cold rolled to a degree tempering it This may be done by a single pass through any dry four-high cold rolling mill capable of precision rolling, which is .what a temper rolling mill is. Naturally, higher tempers may be produced within the temper range common to tin plate, and in all instances higher tempers can be obtained than in the case of the prior art practice. Furthermore, by controlling the nitrogen content to a known value predetermined as giving the; precise temper desired for. a given amount, of

temper cold rolling extension of the strip, it is possible to more accurately control the temper of tin plate, it not having heretofore been the practice to worry about the nitrogen content of tin plate steel. It has been found that a maximum nitrogen content of 011% gives the maximum temper required in the. case of tin. plate or, for that matter, cold reduction tin mill products in general.

The present invention embraces the further step of timing the tempered strip, this being an important consideration because tinning involves the heating of the tin to at least its fusion temperature while it is in contact with the strip, this heating heating the strip also and sometimes being a factor in determining the temper of the finished tin plate, but in the case of the present invention ithas been found that there is no appreciable decrease in the temper of the tin plate obtained by the combined stepsof the nitrogen addition to the steel and the temper cold rolling. A certain increase of hardness is commonly recorded after tinm'ng operation presumably assosiated with the-aging phenomena occurring during melting of coating.

It is to be understood that the manufacture of tin plate starts with the making of the steel from which the ultimate product is processed. The steel making-is an actual step in the making of the tin plate, as are each of the various other steps described in the text previously identified. In the case of the present invention, the tempering of the annealed wide steel strip in tin plate gages, from which cold reduced tin plate must be ultimately produced, goes clear back to the steel making, the addition of the nitrogen at that time being required so that the nitrogen will be in the strip during the tempering step and can cooperate with the temper cold rolling to give a surface hardness having a higher Rockwell value than can' be obtained in the case of steel having exactly the same composition excepting for the lack of the nitrogen, but other- .wise processed exactly like the one containing the defined amount of nitrogen and involving the same temper cold rolling extensions. It is to be understood that the amount of cold working put into the strip during the temper rolling is usually measured in terms of the extension of the strip, and the temper of the strip is usually determined by its surface hardness.

Although the invention has proven its great value in the field of giving the specifically defined temper to tin plate having the specifically defined steel composition, it is generally useful in the art of tempering annealed cold reduced wide steel strip in tin plate gages and made of basic open-hearth steel of tin plate composition which-is naturally low in phosphorus.

Beforeclosing, itmight be well to emphasize that the very low metalloid composition of the specificallydefined steel is demanded partly because of its forming characteristics during the can making and particularly because of its corrosion resistance characteristics, the latter being' important in those instances when the tin coating continuity is not perfect, which it sometimes isnt. Nitrogen has not been found toaffeet the corrosion resistanceand forming characteristics of tin plate to any appreciable degree and so its addition to even the very high quality tinplate steelspecifically defined has been found permissible, this being an important consideration since it is one of the reasons that the use of the nitrogen, instead of phosphorus, for instance, as a tool facilitating the tempering of the strip to the higher tempers, is such a valuable addition to the art with which this invention is concerned. 1

I claim:

The method of producing steel sheets for tin plating having a surface hardness of at least 61 Rockwell T-30, which comprises the steps of adding nitrogen to open hearth. steel in an amount productive of a nitrogen content from 0.008 to 0.011% in the finished steel, the steel otherwise consisting of 0.05 to 0. 2% carbon, 0.25 to 0.60 manganese, maximum of 0.015% phosphorous, maximum of 0.050% sulphur, maximum of 0.010%silicon, maximum of 0.060% copper, maximum of 0.04% nickel, maximum of 0.06% chromium, maximum of 0.02% arsenic,

maximum of 0.05% molybdenum, the remainder, iron, hot-rolling the steel to form a strip, coldrolling the strip to approximately the final gauge thickness of tin plate, annealing the strip whereby its hardness is materially reduced, and temper rolling the strip by only a single pass of the strip through a dry roll temper mill.

ALBERT T. REICHENBACH.

REFERENCES CITED The following references are of record in the file of this patent:

fThe Metallurgy of Deep Drawing and Pressing, Jevons, 2nd ed., 1942, John .Wiley and Sons Inc., N. Y. 0., page 63. 

